Most energy retrofits are bought in the wrong order, windows before attic air sealing being the classic inversion, and the home energy audit exists to fix the sequence: measure the house, find the actual leaks and gaps, and rank the fixes by payback before the money moves. This reference covers the professional audit’s instruments, the DIY version’s honest reach, the incentive landscape, and how a report becomes a plan.
The instruments: blower door and infrared
The blower door is the audit’s centerpiece: a calibrated fan sealed into an exterior doorway depressurizes the house to a standard test pressure and measures the airflow required to hold it, expressing total leakage as a number (air changes per hour at test pressure), the house’s tightness scored on a scale that runs from the sieve-like old stock through code-built to genuinely tight. The number does two jobs: it benchmarks (against code and against the house’s own before-and-after when sealing work is done, effort converted to evidence), and it amplifies, since under depressurization every leak in the house pulls hard enough to find by hand, smoke pencil, or camera, the top-plate and rim suspects confessing in minutes. The infrared camera reads surface temperatures as color: on a cold day (or under blower-door depressurization), missing insulation glows as cold wall and ceiling patches, wind-washed eaves and empty stud bays photograph themselves, and moisture, evaporatively cooled, sometimes appears as the bonus finding that routes through the leak and mold references first. Around the instruments runs the checklist inspection: insulation depths and condition, equipment ages and efficiencies, duct condition per the leakage file, and, in better audits, combustion-safety testing, draft and CO spillage checks on atmospheric appliances, the backdrafting file’s formal version and the test that any meaningful tightening of an older house should trigger anyway.
What the findings usually say
Audit reports repeat themselves across the housing stock, which is itself useful knowledge: attic-plane air leakage and under-depth attic insulation lead nearly every list; the rim joist places; duct leakage dominates houses with attic or crawl ducts; basement and crawl moisture appears as the finding that re-sequences everything (water before insulation, always); and windows, the item homeowners expect to top the list, land far down the payback table, their storm-versus-replacement math being comfort-led rather than energy-led. The report’s value is the sequencing: measures ranked by cost against modeled savings, the cheap-and-large (sealing, attic top-up) ahead of the dear-and-small, with the R-value targets as the destination numbers.
The DIY audit’s honest reach
A homeowner with a free afternoon replicates a real fraction of the value: bill history (a year of usage, weather-normalized by eyeball, flags the outlier house); the attic check, ruler and streak map per that guide; the leak tour, hand and incense stick on a windy day around the standard map, with the kitchen exhaust fan running as a poor man’s blower door; equipment inventory, ages and filters per the lifespan tables; and the moisture walk the other categories script. What DIY cannot do is measure, no leakage number, no before-and-after proof, no infrared wall map, and no combustion instruments, which is the professional visit’s residual case even for the diligent.
Buying it, and the incentive landscape
Audits sell in tiers, walk-through assessments to full instrumented audits, and the buying rules are simple: insist on the blower door (an “audit” without one is a sales walk), prefer credentialed auditors (building-analyst certifications are the trade’s standard), and mind the conflict-of-interest hygiene this site repeats, an auditor who only sells the contractor’s own retrofits is a bid, not a diagnosis, with utility- and program-sponsored audits typically the cleanest and cheapest. The incentive landscape moves but persistently favors this work: utility rebates on audits and sealing, and tax-credit regimes that have repeatedly covered audits, insulation, and equipment, are worth one current search before scheduling, since programs frequently pay for the audit that then unlocks the measure rebates, the paperwork stack that makes the sequenced plan cheaper at every step.
The bottom line
Measure before spending: the blower door numbers the leaks, the camera photographs the gaps, and the report ranks the fixes, which almost always read sealing and attic first, windows last, and moisture before everything. Do the free afternoon version regardless, buy the instrumented version before any major retrofit money moves, and let the before-and-after number, not the brochure, prove the work.